Astronomers Find Rare Beast by New Means

Jan 27, 2010

(PhysOrg.com) -- For the first time, astronomers have found a supernova explosion with properties similiar to a gamma-ray burst, but without seeing any gamma rays from it. The discovery, using the National Science Foundation's Very Large Array (VLA) radio telescope, promises, the scientists say, to point the way toward locating many more examples of these mysterious explosions.

"We think that radio observations will soon be a more powerful tool for finding this kind of supernova in the nearby Universe than gamma-ray satellites," said Alicia Soderberg, of the Harvard-Smithsonian Center for Astrophysics.

The telltale clue came when the radio observations showed material expelled from the supernova explosion, dubbed SN2009bb, at speeds approaching that of light. This characterized the supernova, first seen last March, as the type thought to produce one kind of gamma-ray burst.

"It is remarkable that very low-energy radiation, radio waves, can signal a very high-energy event," said Roger Chevalier of the University of Virginia.

When the nuclear fusion reactions at the cores of very massive stars no longer can provide the energy needed to hold the core up against the weight of the rest of the star, the core collapses catastrophically into a superdense neutron star or black hole. The rest of the star's material is blasted into space in a supernova explosion. For the past decade or so, astronomers have identified one particular type of such a "core-collapse supernova" as the cause of one kind of gamma-ray burst.

Not all supernovae of this type, however, produce gamma-ray bursts. "Only about one out of a hundred do this," according to Soderberg.

In the more-common type of such a supernova, the explosion blasts the star's material outward in a roughly-spherical pattern at speeds that, while fast, are only about 3 percent of the speed of light. In the supernovae that produce gamma-ray bursts, some, but not all, of the ejected material is accelerated to nearly the speed of light.

The superfast speeds in these rare blasts, astronomers say, are caused by an "engine" in the center of the supernova explosion that resembles a scaled-down version of a quasar. Material falling toward the core enters a swirling disk surrounding the new neutron star or black hole. This accretion disk produces jets of material boosted at tremendous speeds from the poles of the disk.

"This is the only way we know that a supernova explosion could accelerate material to such speeds," Soderberg said.

Until now, no such "engine-driven" supernova had been found any way other than by detecting gamma rays emitted by it.

"Discovering such a supernova by observing its radio emission, rather than through gamma rays, is a breakthrough. With the new capabilities of the Expanded VLA coming soon, we believe we'll find more in the future through radio observations than with gamma-ray satellites," Soderberg said.

Why didn't anyone see gamma rays from this explosion? "We know that the gamma-ray emission is beamed in such blasts, and this one may have been pointed away from Earth and thus not seen," Soderberg said. In that case, finding such blasts through radio observations will allow scientists to discover a much larger percentage of them in the future.

"Another possibility," Soderberg adds, "is that the gamma rays were 'smothered' as they tried to escape the star. This is perhaps the more exciting possibility since it implies that we can find and identify engine-driven supernovae that lack detectable gamma rays and thus go unseen by gamma-ray satellites."

One important question the scientists hope to answer is just what causes the difference between the "ordinary" and the "engine-driven" core-collapse supernovae. "There must be some rare physical property that separates the stars that produce the 'engine-driven' blasts from their more-normal cousins," Soderberg said. "We'd like to find out what that property is."

One popular idea is that such stars have an unusually low concentration of elements heavier than hydrogen. However, Soderberg points out, that does not seem to be the case for this supernova.

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User comments : 9

Many new elements, such as nickel are created in the intermediate layers during core collapse, perhaps an unusual high content creation of other, more ferromagnetic elements than nickel, will interact more with the superfast spinning magnetig field of the neutron star remnant and hence be more suspectible to form a swirl

@brant, That day may not be far off. As reported here, http://www.physor...389.html , a second example has come to light, SN 2007gr. Alas, no simultaneous gamma-ray/radio emission, but the sample size is going up.

I have a radical idea that may explain the cause and nature of gamma ray bursts. From the information I have gathered, most are recorded far beyond the visible spectrum which can be observed by an optical telescope. I believe with all my heart that gamma ray bursts are signatures of "big bang" events far beyond our own universe. For all we know in our few hundreds of years knowledge of advanced astronomy and physics, it could be that big bangs are occurring every few days or so far outside our univese itself, meaning that the universe could be more infinite than we think, even containing an infinite number of universes created by big bang events. When they turn on the LHC and gamma rays are emitted in the collisions powerful enough to imitate the state just briefly after the big bang, my hypothesis could prove to be valid.

our universe being the one we know of currently expanding. I believe that the gamma ray bursts are other separate big bangs happening deeper in space, other expansions occurring, beyond the one which contain our galaxies and the optically observable ones. That would explain the massive gamma signatures, which seem to be light years beyond the galaxies we observe through optical telescopes. Why can't we find supernovas that display these gamma signatures? It must be some other event, and I believe that they are signatures of other big bangs, other universes created. I don't know, maybe they are proofs of the multiverse (not parallel, just billions upon billions light years away, more and more big bangs) Does this make sense? I am not an astronomer or scientist, but I'd like to know why I have never heard anyone else hypothesize this to explain these enormous gamma ray signatures. It makes perfect sense to me, if you can fathom just how infinite it is out there.

An alternative scenario suggests that colliding protons could be the source of the VHE gamma rays.

This is a quote from a portion of the above article. The LHC will smash protons, the LHC is supposed to be the experiment to produce.... conditions which mimic the condition moments after the big bang.

senility, quite a few GRBs have reasonably accurate known distances and have been found to reside in the outskirts of galaxies. All GRBs are thought to reside in galaxies or star-forming regions, not beyond them.

Your concept of multiverses sounds like a flavor of 'eternal inflation' that's been kicking around for some time (bubble universe model). Check out the wiki: http://en.wikiped...n_theory .

Common guys we all know that Gamma Ray Bursts are the equivalent of light barrier "sonic booms" when an object/particle is propelled past the speed of light, only possibly due to gravitational/space time distortions similar to the environment within a Super Nova, and creates something like a photon wake, particles that are prevalent in all regions of space....Just kidding of course, but that would be cool!

VLA Rocks and I apologize in advance for not adding to the scientific discussion with my SciFi flights of fancy but there is a whole lot we don't know about GRB.

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